Steering-brake system

Abstract

An off-road vehicle has ground supports on each side which can be simultaneously braked, or independently braked to aid in steering. A braking system includes a brake valve device which feeds high fluid pressure to a pair of reversing valves. The reversing valves deliver the high pressure to respective wheel brake cylinders disposed on opposite sides of the vehicle. The reversing valves and brake valve device are controlled by a common pedal which comprises separately or simultaneously actuable half-pedals. Each half-pedal actuates the brake valve device and a respective reversing valve such that when both half-pedals are depressed the system operates in a dual-sided braking mode, and when only one half-pedal is depressed the system operates in a braked-steering mode. The system can be shifted directly from the dual-sided braking mode to a brake-steering mode by simply releasing one of the half-pedals without having to first release all braking action.

What is claimed is: 
     
       1. Fluid-operated steering brake system for selectively operating one or both of two wheel brake cylinders located on opposite sides of a vehicle, comprising: a high pressure fluid source,   a low pressure fluid region,   a steering-brake unit comprising: a brake-valve device interposed between said pressure source and said wheel brake cylinders, and   first and second reversing valves each interposed between said brake-valve device and a respective one of said wheel brake cylinders for conducting pressurized fluid from said brake valve device to said respective wheel brake cylinder, each of said reversing valves being movable against a restoring force independent of pressurized braking fluid from a first position communicating said respective wheel brake cylinder with said low pressure region to a second position communicating said respective wheel brake cylinder with high pressure fluid received from said brake-valve device, each of said reversing valves comprising: a housing forming a brake-line port communicating with a respective wheel brake cylinder, and a brake pressure port communicating with said brake-valve device for receiving pressurized fluid therefrom,   a movable valve body including spaced lands defining channel means which communicate said brake-line port selectively with said brake pressure port and said low pressure region, one of said lands being configured to overlie said brake pressure port in said first position of said reversing valve to block said brake pressure port from both said brake line port and said low pressure region,   means defining said restoring force for biasing said movable valve body to said first position wherein said one land blocks said brake pressure port from both said brake line port and said low pressure region, and     actuating pedal means comprising half-pedals each associated with said brake valve device and a respective one of said reversing valves, whereby depression of one half-pedal actuates said brake valve device and a respective reversing valve, and depression of both half-pedals actuates said brake valve device and both of said reversing valves, either of two depressed half-pedals being releasable while the other half-pedal remains depressed, whereupon said one land associated with said released half-pedal is moved to said position blocking said brake pressure port from both said brake line port and said low pressure region so that the braking pressure associated with the still depressed half-pedal is not influenced in any way whatsoever.     
     
     
       2. Steering-brake system according to claim 1, wherein said channel means arranged to communicate the respective wheel brake cylinder with the reservoir before communicating said wheel brake cylinder with the high pressure fluid source. 
     
     
       3. Steering-brake system according to claim 2, wherein each valve body contains an internal passage communicating said surface with said low pressure region. 
     
     
       4. Steering-brake system according to claim 3, wherein said brake-valve device is arranged symmetrically relative to said reversing valves. 
     
     
       5. Steering-brake system according to claim 4, wherein said brake-valve device includes a valve body arranged to be displaced by said pedal means against the force of a restoring spring and the brake pressure feedback. 
     
     
       6. Steering-brake system according to claim 5, wherein said pedal means is symmetric with a reference plane extending midway between said restoring valves. 
     
     
       7. Steering-brake system according to claim 1 including a panel in said vehicle, said pedal means being pivotably connected to said panel, said steering-brake unit comprising a housing encasing said brake valve device and said reversing valves, said housing attached to said panel. 
     
     
       8. Steering-brake system according to claim 7 including adjusting means for adjusting the location of said housing relative to the pivot connection of said pedal means with said panel. 
     
     
       9. Steering-brake system according to claim 8, wherein said adjusting means comprises threaded bolts carried by one of said panel and housing and having an end bearing against the other of said panel and housing to move the latter when rotated. 
     
     
       10. Steering-brake system according to claim 1, wherein said pedal means is T-shaped and includes a cross-bar portion defined by aligned portions of both half-pedals, said cross-bar arranged to actuate said reversing valves and said brake valve device. 
     
     
       11. Steering-brake system according to claim 10 including a shaft common to said half-pedals for pivotably supporting said half-pedals. 
     
     
       12. Steering-brake system according to claim 1 including an adjustable stop member for defining a rest position of said half-pedals. 
     
     
       13. Steering-brake system according to claim 1, wherein said brake valve device includes a slidable valve body, the axes of all of said valve bodies disposed in a common plane. 
     
     
       14. Steering-brake system according to claim 1, wherein said brake valve device is constructed such that the pressure intensity of the high pressure fluid delivered by said brake valve device varies in accordance with the amount of depression of said pedal means. 
     
     
       15. Steering-brake system according to claim 1, wherein said high-pressure source comprises a source of hydraulic fluid.